This invention relates to high performance electronic gain and noise control circuits for analog record and playback devices. High performance is used here in the sense of providing reproduction of analog information, typically audio signals, with relatively true fidelity over a selected frequency range and a selected dynamic range. It also includes the introduction of selected control of the analog reproduction to avoid distortion and listener distraction that otherwise occur during certain movements of a magnetic medium, e.g. tape rewind.
More particularly, the invention provides a magnetic record/playback system, sometimes referred to simply as a recorder, that provides multiple controls of gain and of noise. Specific control features of the recorder are the cancellation of noise that the playback transducer unit picks up, the limiting of record gain in response to excessive signal amplitudes, and the muting of playback during certain operations. Further, the invention enables these features to be provided together with the conventional noise reduction that a compandor makes possible.
High performance magnetic record/playback systems for analog informatiion are well known, and many--commonly termed tape decks--are commercially available, especially for audio reproduction. "The Hi-FI Book," 1979, available from Tech Hi-Fi and published by Stereo Components Systems, Inc., describes illustrative, present-day commercially-available consumer tape decks as well as dynamic compandors. It is understood that this audio equipment employs a variety of electronic control circuits that provide gain control noise reduction, limiting, dynamic expansion, dynamic compression, equalization, and perhaps other functions considered to enhance the performance of audio reproduction with a magnetic storage medium.
The application of a dynamic compandor to provide high performance electronic gain control in consumer and other analog equipment is also known. See for example the "Signetics Analog Data Manual" available from Signetics Corporation, Sunnyvale, Calif. Note in particular pages 482, 483, and 794-805 of that publication.
With this state of the art, it is an object of this invention to provide improved gain and noise control in a high performance record/playback system. It is also an object of the invention to provide a multiple of such control features with an economy of circuit stages.
A particular object of the invention is to provide a magnetic recorder arrangement that cancels noise picked up by the playback transducer unit in a manner suitable for use in a variety of record/playback systems.
Another particular object is to provide a record/playback system having a compandor and which also provides record gain limiting and playback muting.
A further object of the invention is to provide high performance electronic circuits which readily provide a combination of the foregoing features.
It is also an object to provide circuits which provide the foregoing features and are suited for consumer electrical products and in particular which are compatible with multi-media equipment. Thus it is an object to provide the foregoing electronic gain and noise control in equipment which provides a visual display together with audio reproduction. One particular instance of this equipment is photographic projection combined with audio reproduction, as in a sound movie projector.
Other objects of the invention will in part be set forth below and will in part be obvious from the following description.